| Internet-Draft | BIER Babel extensions | May 2021 |
| Zhang & Przygienda | Expires 11 November 2021 | [Page] |
BIER introduces a novel multicast architecture. It does not require a signaling protocol to explicitly build multicast distribution trees, nor does it require intermediate nodes to maintain any per-flow state.¶
Babel defines a distance-vector routing protocol that operates in a robust and efficient fashion both in wired as well as in wireless mesh networks. This document defines a way to carry necessary BIER signaling information in Babel.¶
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[RFC8279] introduces a novel multicast architecture. It does not require a signaling protocol to explicitly build multicast distribution trees, nor does it require intermediate nodes to maintain any per-flow state. All procedures necessary to support BIER are abbreviated by the "BIER architecture" moniker in this document.¶
[RFC8966] define a distance-vector routing protocol under the name of "Babel". Babel operates in a robust and efficient fashion both in ordinary wired as well as in wireless mesh networks.¶
The terminology of this documents follows [RFC8279], [RFC6126], [RFC7557] and [RFC8966].¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
In case a router is configured with BIER information, and Babel is the routing protocol used, such a router MAY use Babel protocol to announce the BIER information using the BIER sub-TLV specified below.¶
BFR-prefix and according information is carried in a Babel Update TLV per [RFC8966]. A new sub-TLV is defined to convey further BIER information such as BFR-id, sub-domain-id and BSL. Two sub-sub-TLVs are carried as payload of BIER sub-TLV.¶
The mandatory bit of BIER sub-TLV should be set to 0. If a router cannot recognize a sub-TLV, the router MUST ignore this unknown sub-TLV.¶
The BIER sub-TLV format aligns exactly with the definition and restrictions in [RFC8401] , [RFC8444] and [I-D.ietf-bier-ospfv3-extensions]. It is a sub-TLV of Babel update TLV. The prefix MUST NOT be summarized and the according sub-TLV MUST be treated as optional and transitive.¶
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BAR | IPA | subdomain-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BIER sub-TLV
¶
The BIER MPLS Encapsulation sub-sub-TLV can be carried by BIER sub-TLV. The format and restrictions are aligned with [RFC8401], [RFC8444] and [I-D.ietf-bier-ospfv3-extensions]. This sub-sub-TLV carries the information for the BIER MPLS encapsulation including the label range for a specific BSL for a certain <MT,SD> pair.¶
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS Encapsulation sub-sub-TLV
¶
The BIER non-MPLS Encapsulation sub-sub-TLV can be carried by BIER sub-TLV. The format and restrictions are aligned with [I-D.ietf-bier-lsr-ethernet-extensions]. This sub-sub-TLV carries the information for the BIER MPLS encapsulation including the label range for a specific BSL for a certain <MT,SD> pair.¶
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI | BIFT-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|BS Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: non-MPLS Encapsulation sub-sub-TLV
¶
The BIER IPv6 transportation sub-sub-TLV can be carried by BIER non-MPLS Encapsulation sub-sub-TLV. The format and restrictions are aligned with [I-D.zhang-bier-bierin6]. A node that requires IPv6 encapsualtion MUST advertise the BIER IPv6 transportation sub-sub-TLV according to local configuration or policy in the BIER domain to request other BFRs to always use IPv6 encapsulation.¶
The format is the same with the definition in section 4.1, [I-D.zhang-bier-bierin6].¶
Since Babel is performing a diffusion computation, support for different tree types is not as natural as with link-state protocols. Hence this specification is assuming that normal Babel reachability computation is performed without further modifications.¶
BIER architecture does not rely on all routers in a domain performing BFR procedures. How to support tunnels that will allow to tunnel BIER across such routers in Babel is for further study.¶
TBD¶
A new type of Babel update sub-TLV needs to be defined for BIER information advertisement.¶